The present invention relates to a microwave transmission system for multipath transmission operating according to the angle diversity principle and more particularly to an improved exciter and mode coupler for such a system.
German Patent No. 2,626,925, issued Jan. 8, 1981, discloses a method which reduces the effects of statistical fluctuations in propagation on microwave transmission paths in that, in order to obtain angle diversity signals, the received energy of more than one mode is coupled in the waveguide-fed receiving antenna. This method is based on the fact that during a very large percentage of the transmission duration, at least one mode furnishes an evaluatable received signal. With this known method, it is possible to construct, for example with a single receiving antenna, a double angle diversity system which feeds the two received signals obtained from the different modes to separate receivers and derives therefrom the best signal.
It is also possible to employ a plurality of antennas or a plurality of exciters in one antenna for multipath transmission processes. This type of arrangement, however, is very complicated and, if a plurality of exciters are used in our antenna, leads to difficulties in the transmission of the transmitted signal because the spread angle between the individual radiation lobes is much too large, for example for troposcatter transmission.